Various cable-driven arm-reciprocating systems are available for transferring nuclear fuel bundles from a nuclear reactor pool to a spent fuel storage pool. During refueling it is necessary to transfer the fuel bundles from the reactor core to a spent fuel building flooded with water. The spent fuel bundles must remain submerged for an extended period as they cool and during this time the reactor is normally returned to operation. Therefore the spent fuel bundles and their pool must be located apart from the reactor container vessel. Access to the reactor container vessel is through an elongated transfer tube in the vessel wall.
Some prior fuel transfer systems have relied strictly on rectilinear motion of the fuel transfer carriage assembly. An example is that described in U.S. Pat. No. 3,637,096 wherein some of the cable sheaves of the system are permanently mounted in the reactor pool. The same is true of a fuel transfer machine described in U.S. Pat. No. 4,069,766. Not only is it a disadvantage to have some of the sheaves of the system in the transfer tube or reactor vessel but with purely rectilinear motion of the system the spent fuel pool must be large enough to accommodate the full stroke of the apparatus.
The prior art also includes a form of fuel bundle transfer apparatus wherein an arm having end-to-end articulated forward and rearward portions is longitudinally translated between an extended position where the arm portions are aligned on a straight track and a retracted postition where the rearward arm portion is angled on a curved track out of alignment with the forward arm portion. However the cable reeving system for this prior art apparatus was deficient. It consisted of a cable attached to the forward and rearward ends of the rearward arm portion. A first run of the cable extended forwardly from a rearward arm attachment over a forward fixed-axis sheave and also over a pick-up roller on the forward end of the rearward arm potion when the pick-up roller was rearwardly of forward fixed-axis sheave. A second run extended rearwardly from the forward fixed-axis sheave around a rearward fixed-axis sheave to a winch drum. A third run extended from the winch drum around another rearward fixed-axis sheave and forward to attachment with the forward end of the rearward arm portion.
The difficulty with this reeving system was that it lacked cable tension control. After prolonged use the cable would tend to loosen and even an occasion come off one or more of the sheaves. It is the principal purpose of the present invention to improve upon such a cable reeving system so that it includes the needed tension control.